Dimethyl ether is a commodity in the chemical industry, widely used as a starting material in the preparation of other chemicals, e.g., dimethyl sulfate, and more recently, as a propellant in aerosol containers.
One of the commonly used methods for preparing dimethyl ether is the catalytic dehydration of methanol, using a phosphoric acid-alumina catalyst.
While that process is generally satisfactory, the catalyst has a tendency to coke, which makes it necessary to replace it more frequently than is desirable. By "coke" is meant the phenomenon by which the surface of the catalyst becomes coated with carbon, thus blocking its pores and reducing its effectiveness.
It has now been found that this coking can be minimized if, instead of the phosphoric acid-alumina catalyst, one uses an aluminosilicate catalyst containing 1-20% silica and 80-99% alumina. Surprisingly, use of such a catalyst according to the invention not only reduces the amount of coking but also significantly increases the rate of the dehydration reaction over that obtained with the phosphoric acid-alumina catalyst, and greatly reduces the number and amounts of byproducts formed, notably hydrogen, carbon monoxide, methane, ethane, propane, ethylene, propylene and various ethers having high boiling points.